TCallbackEventParameter provides the parameter passed during the callback request in the CallbackParameter property. The callback response content (e.g. new HTML content) must be rendered using an THtmlWriter obtained from the NewWriter property, which returns a NEW instance of TCallbackResponseWriter.

Each instance TCallbackResponseWriter is associated with a unique boundary delimited. By default each panel only renders its own content. To replace the content of ONE panel with that of rendered from multiple panels use the same writer instance for the panels to be rendered.

The response data (i.e., passing results back to the client-side callback handler function) can be set using ResponseData property.